Side view light emitting diode package

ABSTRACT

A side view LED package for a backlight unit includes a package body having a cavity with an inclined inner sidewall, first and second lead frames arranged in the package body, the cavity of the package body exposing a portion of at least one of the first and second lead frames placed in a bottom of the cavity to outside, a light emitting diode chip mounted on the bottom of the cavity to be electrically connected to the first and second lead frames, and a transparent encapsulant arranged in the cavity surrounding the light emitting diode chip. The cavity has a depth larger than a mounting height of the light emitting diode chip and not exceeding six times of the mounting height. The height of the sidewall is shortened to improve beam angle characteristics of emission light, increase light quantity, and prevent a molding defect of the sidewall.

CLAIM OF PRIORITY

This application claims the benefit of Korean Patent Application No.2005-113834 filed on Nov. 25, 2005, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high power Light Emitting Diode (LED)package, particularly, in which the height of a sidewall is shortened toimprove beam angle characteristics of emission light, increase lightquantity, and prevent a molding defect of the sidewall.

2. Description of the Related Art

A Liquid Crystal Display (LCD) does not have a light source of its own,and thus requires an external illumination, which is generally referredto as a backlight unit. The backlight unit illuminates the LCD from theback and uses a Cold Cathode Fluorescent Lamp (CCFL) or an LED as alight source.

FIGS. 1 and 2 show a general backlight unit 1 in use for the LCD.Referring to FIGS. 1 and 2, the backlight unit 1 includes a plurality ofLED packages 10, a light guide plate 20, a reflector sheet 24, adiffuser sheet 26 and a pair of prism sheets 28. With this arrangement,light incident from the LED package 10 into the light guide plate 20 isdirected to an LCD panel 30 above, providing backlighting to the LCD.

Describing it in more detail, the LED package 10 includes an LED chip12, cathode and anode leads 14 for supplying power to the LED chip 12seated thereon, a package body 16 holding the leads 14 and anencapsulant 18 of a transparent resin filled into a cavity C of thepackage body 16 to encapsulate the LED chip 12 as shown in FIGS. 3 and4.

Light beams L1 to L3 generated from the LED chip 12 are introduced intothe light guide plate 20, and travel inside the light guide plate 20before scattered at a dot pattern 22. When the light beam L1 isscattered upward at the dot pattern 22, it exits the light guide plate20, thereby reaching the LCD panel 30 through the diffuser plate 26 andthe prism sheet 28.

Describing the LED package 10 in more detail with reference to FIGS. 3and 4, the cavity C of the LED package 10 where the encapsulant 18 isfilled has a depth d generally of 600 μm to 650 μm. The depth d isdetermined mainly by the mounting height t of the LED chip 12, theheight h1 of a loop of a wire W and the height h2 from the wire W up tothe top surface of the encapsulant 18.

When the depth d has a larger value, the height h1+h2 from the topsurface of the LED chip 12 to the top surface of the encapsulant 18 alsoincreases. This, however, brings in following problems.

First, this restricts the beam angle α of the light emitted out of theLED package 10. When the beam angle α is smaller, the backlight unit 1should use the more LED packages 10.

Second, as can be seen from FIG. 5, when light beams L generated fromthe LED chip 12 are emitted in the direction of arrow A, a partial lightbeam L1 collides against a sidewall 17 of the LED package 10. Whencollided against the side wall 17, the light beam 17 is lost due to forexample absorption/scattering. This reduces the entire light quantityemitted out of the LED package 10. The light quantity decreases morewhen the sidewall 17 is higher, that is, the cavity depth d in FIG. 4 islarger.

Third, the higher sidewall 17 may cause more easily a molding defectsuch as a void in an upper or lower portion of the sidewall 17. This maytake place particularly in a portion designated with the reference signI in FIG. 3. With the molding defect, the LED package 10 is degraded inperformance, and sometimes, should be discarded.

SUMMARY OF THE INVENTION

The present invention has been made to solve the foregoing problems ofthe prior art and therefore an aspect of the present invention is toprovide a side view LED package in which the height of a sidewall isshortened to improve beam angle characteristics of emission light,increase light quantity, and prevent a molding defect of the sidewall.

According to an aspect of the invention, a side view LED package in usefor a backlight unit includes a package body having a cavity with aninner sidewall inclined between a bottom and a top; first and secondlead frames arranged in the package body, the cavity of the package bodyexposing a portion of at least one of the first and second lead framesplaced in the bottom of the cavity to outside; a light emitting diodechip mounted on the bottom of the cavity to be electrically connected tothe first and second lead frames; and a transparent encapsulant arrangedin the cavity surrounding the light emitting diode chip. The cavity hasa depth that is larger than a mounting height of the light emittingdiode chip and does not exceed six times of the mounting height.

The mounting height of the light emitting diode chip may be from 50 μmto 200 μm. Here, the depth of the cavity is preferably from 200 μm to480 μm.

According to another aspect of the invention, there is provided anapproach to reduce the height of the wires since the wires act as afactor limiting the reduction of the depth of the cavity. The side viewLED package according to this aspect of the invention includes a packagebody having a cavity with an inner sidewall inclined between a bottomand a top; first and second lead frames arranged in the package body,the cavity of the package body exposing a portion of at least one of thefirst and second lead frames placed in the bottom of the cavity tooutside; a light emitting diode chip mounted on the bottom of the cavityto be electrically connected to the first and second lead frames; atransparent encapsulant arranged in the cavity surrounding the lightemitting diode chip; and wire for electrically connecting the lightemitting diode chip to at least one of the first and second lead frames,the wire having one end connected to a bump ball of the light emittingdiode chip and the other end stitch-bonded to the lead frame. Here, thedepth of the cavity is from 200 μm to 480 μm.

In this case, the height of the wire from the top of the LED chip to thetop of the wire can be reduced preferably to 100 μm or less, and morepreferably to the order of 70 μm. Thus, the afore-described bonding isadvantageous to set the cavity depth in a small value.

According to further another aspect of the invention, there is providedan approach to design a cavity suitably in view of the convenience inthe filling process of transparent and encapsulating liquid resin withrespect to a relatively low depth and the formability of molding for apackage body. The side view LED package of this aspect includes apackage body having a cavity with an inner sidewall inclined between abottom and a top; first and second lead frames arranged in the packagebody, the cavity of the package body exposing a portion of at least oneof the first and second lead frames placed in the bottom of the cavityto outside; a light emitting diode chip mounted on the bottom of thecavity to be electrically connected to the first and second lead frames;and a transparent encapsulant arranged in the cavity surrounding thelight emitting diode chip. Here, the depth of the cavity may be from 200μm to 480 μm, the cavity may have a first width in a shorter axialdirection and a second width in a longer axial direction perpendicularto the shorter axial direction, and the second width of the cavity maybe from 1.5 mm to 1.7 mm at the bottom of the cavity. In view of theinclination angle of the sidewall, the second width of the cavity ispreferably from 2.0 mm to 2.5 mm at a top end of the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a perspective view illustrating a general backlight unitincorporating side view LED packages;

FIG. 2 is a perspective plan view of the backlight unit shown in FIG. 1;

FIG. 3 is a front elevation view of a conventional side view LEDpackage;

FIG. 4 is a cross-sectional view taken along the line 4-4 of FIG. 3;

FIG. 5 is a cross-sectional view illustrating light absorption bysidewalls in the LED package shown in FIG. 4;

FIG. 6 is a cross-sectional view illustrating an LED package of theinvention;

FIG. 7 is a cross-sectional view illustrating an exemplary wire bondingwithin the LED package of the invention;

FIG. 8 is a cross-sectional view illustrating another exemplary wirebonding within the LED package of the invention;

FIG. 9 is a cross-sectional view illustrating light emission from theLED package of the invention;

FIG. 10 is a graph, illustrating brightness levels according to severalversions of the LED package of the invention;

FIG. 11 is a graph illustrating beam angle characteristics of the LEDpackage of the invention;

FIG. 12 is a graph illustrating beam angle characteristics of aconventional LED package;

FIGS. 13 to 15 are graphs illustrating beam angle characteristicsaccording to several versions of the LED package of the invention; and

FIG. 16 is a graph illustrating the percent defective in injectionmolding of package bodies according to the width of recesses in LEDpackages.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown.

FIG. 6 is a cross-sectional view illustrating an LED package 100according to an embodiment of the invention.

Referring to FIG. 6, the side view LED package 100 of the invention isapplied to the backlight unit 1 as shown in FIG. 1. The LED package 100includes an LED chip 102, first and second lead frames 104 for supplyingpower to the LED chip 102 seated thereon, a package body 106injection-molded to hold the first and second lead frames 104 and anencapsulant 108 of a transparent resin filled in a cavity C of thepackage body 106 to encapsulate the LED chip 102.

The LED package 100 according to this embodiment of the invention has animprovement in the cavity C in order to improve light quantity and beamangle. The height of a sidewall of the LED package 100, that is, thedepth d of the cavity C is set to be larger than the height t of the LEDchip 102 but not exceeding six (6) times of the same. Considering atypical LED chip mounting height (e.g., in the range from 50 μm to 200μm), the depth d of the cavity C is set to be 200 μm to 480 μm. This isremarkably smaller than the cavity depth (600 μm to 650 μm) of theafore-described conventional LED package 10 (see FIG. 4).

Accordingly, the beam angle of light emitted out of the LED package 100can be improved to be advantageously applied to the backlight unit.Describing it in more detail, in case of application to the backlightunit, LED packages with a larger beam angle can be decreased in numberwith respect to those with a smaller beam angle.

This structure also lowers the probability of light generated from theLED chip 102 to collide against the sidewall 107 so that lightabsorption/scattering by the sidewall 107 can be reduced to increaselight quantity emitted out of the LED package 100.

FIG. 9 shows light emission from the LED package 100 of this embodiment.As shown in FIG. 9, when light beams L are emitted from the focus F ofthe LED chip 102, most of the light beams L advance in the direction ofarrow A without colliding against the sidewall 107. This can reducelight loss greatly, thereby raising light intensity greatly.

Furthermore, with reduction in the depth d of the cavity C, the sidewall107 is also lowered in height. This can advantageously prevent a moldingdefect designated with the reference sign I in FIG. 3 that otherwisewould readily take place in the injection molding of the package body.

With the LED package 100 of this embodiment adjusted in the depth d ofthe cavity C, it is possible to improve the performance of the LEDpackage 100 as a light source and reduce any defects in the injectionmolding as well.

In general, as shown in FIG. 6, the side view LED package 100 has anelectric connection of the LED chip 102 with the first and second LEDframes 104 that can be realized by wires W.

In this case, the cavity depth is required to be larger than the wireheight h11+t so that the wires W provided as an electrically connectingmember can be arranged inside the transparent encapsulant. Like this,the wires W become a factor limiting the reduction of the depth d of thecavity C. In order to overcome this problem, an aspect of the inventionprovides an approach to reduce the height of the wires.

Now a wire bonding inside the LED package will be described withreference to FIGS. 7 and 8.

Each of FIGS. 7 and 8 shows an LED chip 102 mounted on a lead frame 104by means of an adhesive layer 103.

Referring to FIG. 7, the wire W is connected at one end to the LED chip102 with a bump ball B. At the other end, the wire W is terminated witha stitch S that is connected to the lead frame 104.

With this type of wire bonding, the height h′11 of the wire W from theLED chip 102 to the top of the wire loop can be decreased to 150 μm.However, it is difficult to decrease the height h′11 of the wire Wfurther. This is because the wire should be looped to a specific heightabove the LED chip 102 after bonded the LED chip 102.

On the contrary, referring to FIG. 8, the wire W is bonded at one end tothe lead frame 104 with a bump ball B and terminated at the other endwith a stitch S on the LED chip 102 to electrically connect the LED chip102 with the lead frame 104.

In this arrangement, the height h″11 of the wire above the LED chip 102can be further reduced from that shown in FIG. 7. This is because, whenthe wire W is looped upward to a total height (=h″11+t) from the leadframe 104 to which the wire W is bonded with the bump ball B, themounting height t of the LED chip is included in the total height of thewire loop.

That is, when the wire bonding processes shown in FIGS. 7 and 8 arecarried out with the same equipment and method, the total height h″11+tof the wire W as shown in FIG. 8 can be substantially the same as thepartial height h′11 of the wire above the LED chip 102 as shown in FIG.7. Accordingly, the cavity depth d of FIG. 8 can be set to be remarkablysmaller than that of FIG. 7.

In the wire bonding of FIG. 8, the height h″11 of the wire W from theLED chip 102 can be reduced to the order of 100 μm or less, andpreferably, to about 70 μm.

With the wire bonding as described above, it is possible to reduce theheight necessary for the wire bonding remarkably from the prior art andthus decrease the cavity depth d remarkably.

Accordingly, with the wire bonding structure as shown in FIG. 8, it ispossible to easily produce a side view LED package having a cavity depthd in the range from 200 μm to 480 μm.

The cavity depth d may be preferably 200 μm or more to ensure a suitablethickness of transparent resin, which will encapsulate the LED chipand/or wires not to be exposed to the external environment, consideringthe total height h″11+t of the wire W or the maximum mounting height ofthe LED chip in a case where the wire bonding structure is not adopted.

Considering a following transparent resin filling process, to furtherpromote effects resulting from the improvement in the cavity, the cavitydepth is more preferably 250 μm to 400 μm, and still more preferably onthe order of 300 μm.

As another aspect, the invention provides an approach to suitablycontrol the width of the cavity in view of the resin filling process forthe transparent encapsulant and the percent defective in the injectionmolding of the package body.

Referring to the side view LED package 100 shown in FIG. 6, it is moredesirable that the cavity depth d is smaller. However, as a drawback,the smaller cavity depth d causes difficulty to the resin fillingprocess. This as a result requires precise procedures to fill thetransparent resin such as silicone into the cavity C to form thetransparent encapsulant 108. In particular, since the entire cavity Cbecomes smaller when the cavity depth d is reduced, it is required toprecisely inject a small amount of resin into the cavity.

In general, the cavity has a first width in the shortest width direction(i.e., transverse width) and a second width P in the longest widthdirection (i.e., longitudinal width) perpendicular to the transversedirection. In this case, the resin filling process can be carried outefficiently.

However, when the longitudinal width of the cavity is increasedexcessively, injection molding may readily cause defects to the packagebody 107 as illustrated in and described with reference to FIG. 3.Accordingly, the longitudinal width of the cavity is preferablyrestricted to a predetermined range.

The inventors have investigated the percent defective in the injectionmolding of resultant packages by increasing the cavity longitudinalwidth from 2.0 mm to 3.0 mm with other factors remaining the same. As aresult, it was found that the percent defective in the injection moldingsharply rises when the cavity longitudinal width P1 exceeds 2.5 mm as inthe graph shown in FIG. 16.

In view of such results, the longitudinal width P1 at the top of thecavity C is set preferably from 2.0 mm to 2.5 mm. Considering the angleof the inner sidewall inclined for reflection, the longitudinal width P2at the bottom of the cavity C is set preferably from 1.5 mm to 1.7 mm.

Like this, when the cavity longitudinal width P (P1, P2) is controlledtogether with the cavity depth d, a more excellent side view LED packagecan be provided.

FIG. 10 is a graph illustrating brightness levels according to severalversions of the LED package of the invention. LED packages used in thisexperiment had a following structure: an LED mounting height of about 80μm; and a wire height (up to the top of the wire including the LEDmounting height) of about 170 μm to 180 μm.

In FIG. 10, A indicates an LED package with a cavity depth of 300 μm andcavity longitudinal widths 1.5 mm (bottom) and 2.0 mm (top); B indicatesan LED package with a cavity depth of 300 μm and cavity longitudinalwidths 1.5 mm (bottom) and 2.2 mm (top); C indicates an LED package witha cavity depth of 300 μm and cavity longitudinal widths 1.7 mm (bottom)and 2.2 mm (top); D indicates an LED package with a cavity depth of 400μm and cavity longitudinal widths 1.5 mm (bottom) and 2.2 mm (top); andE indicates an LED package with a cavity depth of 400 μm and cavitylongitudinal widths 1.7 mm (bottom) and 2.2 mm (top). Here, theindividual packages used an LED chip having 18 mW output.

As seen from FIG. 10, it is brighter when the cavity depth is larger. Ofcourse, the angle of the sidewall, that is, the ratio of the cavitylongitudinal width at the bottom to the cavity longitudinal width at thetop also affects the brightness. However, the width ratio is relativelyinsignificant compared to the cavity depth.

FIG. 11 is a graph illustrating beam angle characteristics of an LEDpackage of the invention, and FIG. 12 is a graph illustrating beam anglecharacteristics of a conventional LED package. The LED packages used inFIGS. 11 and 12 had a chip mounting height and a wire height similar tothose shown in FIG. 10.

As a difference, the side view LED package of the invention had a cavitydepth of 300 μm and the conventional side view LED package had a cavitydepth of 650 μm.

Observing beam angle characteristics of the LED packages, the LEDpackage of the invention had beam angles of 114.2° in X axis (widthdirection of the LED package) and 115.3° in Y axis (thickness directionof the LED package perpendicular to the width direction). On the otherhand, the conventional LED package had beam angles of 111.5° in X axisand 91.7° in Y axis. From these numeric values, it is apparent that thebeam angle characteristics were improved in the invention.

FIGS. 13 to 15 are graphs illustrating beam angle characteristicsaccording to several versions of the LED package of the invention.

Three versions of the LED package of the invention were produced andbeam angles according to the individual LED package versions wereobserved.

The LED package in FIG. 13 had a cavity depth of 500 μm, in whichtransparent resin was NMW114WA available from Otsuka of Japan was andfluorescent material was G3, which were mixed at a ratio of 12:1. Thebeam angles A of the LED package observed in FIG. 13 were 119.6° in alonger axis, that is, the width direction of the LED package, and 105.8°in a shorter axis.

The LED package in FIG. 14 had a cavity depth of 400 μm, in whichfluorescent material transparent resin was NMW114WA available fromOtsuka of Japan was and fluorescent material was G3, which were mixed ata ratio of 12:1. The beam angles A of the LED package observed in FIG.13 were 121.6° in a longer axis, that is, the width direction of the LEDpackage, and 114.8° in a shorter axis.

The LED package in FIG. 15 had a cavity depth of 400 μm, in whichtransparent resin was NMW114WA available from Otsuka of Japan andfluorescent material was TAG, which were mixed at a ratio of 12:1. Thebeam angles A of the LED package observed in FIG. 13 were 120.7° in alonger axis, that is, the width direction of the LED package, and 118.7°in a shorter axis.

In the side view LED package of the invention as described hereinbefore,the height of the sidewall is shortened to improve beam anglecharacteristics of emission light, increase light quantity, and preventa molding defect of the sidewall.

While the present invention has been described with reference to theparticular illustrative embodiments and the accompanying drawings, it isnot to be limited thereto but will be defined by the appended claims. Itis to be appreciated that those skilled in the art can substitute,change or modify the embodiments into various forms without departingfrom the scope and spirit of the present invention.

1-12. (canceled)
 13. A side view light emitting diode packagecomprising: a package body having a cavity with an inner sidewallinclined between a bottom and a top; first and second lead framesarranged in the package body, a portion of each of the first and secondlead frames placed in the bottom of the cavity; a light emitting diodechip mounted on the bottom of the cavity to be electrically connected tothe first and second lead frames; and at least one wire for electricallyconnecting the light emitting diode chip to at least one of the firstand second lead frames, wherein the wire is arranged in such a fashionthat a height from a top surface of the light emitting diode chip to atop end of the wire is 100 μm or less; and, wherein the mounting heightof the light emitting diode chip is from 50 μm to 200 μm, and the depthof the cavity is from 200 μm to 480 μm.
 14. The side view light emittingdiode package according to claim 13, wherein the wire having one endconnected to a bump ball of the lead frame and the other endstitch-bonded to the light emitting diode chip
 15. The side view lightemitting diode package according to claim 13, wherein a transparentencapsulant formed in the cavity surrounding the light emitting diodechip and comprising silicone resin.